1. Field of the Invention
The present invention relates to a shaft-drive-type power transmission device of a vehicle. In particular, the shaft-drive type power transmission device transmits a rotational driving force of an engine to an input shaft on a wheel side from an output shaft on an engine side by way of a drive shaft.
2. Background of the Invention
A shaft-drive-type power transmission device that connects one end of a propeller shaft to an output shaft on an engine side by way of a universal joint and connects another end of the propeller shaft to an input shaft on a wheel side by way of another universal joint has been practically used.
Such a shaft-drive-type power transmission device has been known, which divides a propeller shaft in two and interposes a damper mechanism for dampening an impact between two divided propeller shafts (for example, see JP-A-56-163995 (page 4, FIG. 2)).
A technique of JP-A-56-163995 will now be explained. The conventional shaft-drive-type power transmission device is a shaft-drive-type power transmission device for a hull and is constituted of an output shaft (first shaft) which extends from an engine, the propeller shaft (second shaft) which has one end thereof connected to the output shaft by way of one universal joint, and an input shaft (third shaft) which is connected to another end of the propeller shaft by way of another universal joint.
The propeller shaft is constituted of an output-shaft-side shaft portion that is connected to one universal joint, an input-shaft-side shaft portion that is connected to another universal joint, and a damper mechanism that is interposed between these shaft portions.
However, although the conventional shaft-drive-type power transmission device can dampen an impact attributed a torque transmitted from the output shaft to the input shaft by way of the propeller shaft by the damper mechanism, it is necessary to ensure the rigidity of the propeller shaft, a final reduction gear and the like by estimating a case that a relatively large back torque or the like (excessively large torque) is applied to the propeller shaft, the final reduction gear and the like.
In general, it is known that when two shafts are connected by a universal joint and the shaft-drive-type power transmission device is used in a state these shafts are bent by the universal joint, a rotational speed is changed. Accordingly, in connecting one end of the second shaft to the first shaft by way of one universal joint and connecting a third shaft to another end of the second shaft by way of another universal joint, it may be possible to cancel the change of the rotational speed generated by one universal joint with the change of the rotational speed generated by another universal joint by selectively determining a phase between one universal joint and another universal joint.
In the conventional shaft-drive-type power transmission device, since the damper mechanism is interposed in the propeller shaft (second shaft), there exists a drawback that phases of one universal joint and another universal joint which are set for canceling the change of the rotational speed are displaced from each other.
Further, in the conventional shaft-drive-type power transmission device, due to the provision of the damper mechanism in the propeller shaft, there exists a possibility that an unsprung weight is increased.
That is, there exists a demand for a shaft-drive-type power transmission device of a vehicle which can prevent an excessively large torque from being applied to a power transmission path, can prevent phases of one universal joint and another universal joint from being displaced from each other, and can suppress the increase of an unsprung weight.